In the above-mentioned parent application Ser. No. 071,835, an improved HDR machine is disclosed. That application sets forth the general prior art HDR machines and describes those prior art machines as having a radioactive source assembly disposed in a source channel (a channel in a shielding block of conventional design), a guide tube connected to a first end of the source channel, and a second end thereof being disposable in the animal body at the site of intended therapy. A source assembly transport thread (cable) is connected to the source assembly and to a source assembly drive means for driving the source assembly from the source channel and toward the second end of the guide tube, which second end will be the site of intended therapy. This is the same general prior art HDR machine, as described above.
The improvement in that parent application is that of providing a test assembly disposed in a separate test channel. A connector tube connects at a first end to the test channel and at a second end to a connector disposed in the guide tube. Thus, a juncture is formed at the connector between the guide tube and the connector tube. A test assembly transport thread (cable) is attached at one end to the test assembly and at another end to a test assembly drive means for driving the test assembly from the test channel, through the connector tube and connector, and toward the second end of the guide tube. In this arrangement, the source assembly and the test assembly are alternatingly drivable toward the second end of the guide tube. A detector means is provided for detecting the presence of a test assembly or the source assembly in the guide tube between the juncture and the second end of the guide tube.
Thus, in this arrangement, the test assembly is driven through the connector tube and guide tube and past the detector, which is generally at the juncture between the connector tube and the guide tube. The detector will determine when the test assembly passes that juncture. Since the guide tube between the juncture and the site of intended therapy will be a common path for both the test assembly and the source assembly, accurately measuring the excursion of the test assembly from the detector to the site of intended therapy (confirmed by X-ray or the like) will give a very precise measurement of the excursion necessary for the source assembly once that source assembly also passes the detector and into the common pathway guide tube. The guide tube can remain essentially in place on the patient during both when the test assembly is operated and when the source assembly is operated, and, hence, disturbing the common pathway guide tube is not necessary. This gives a very precise positioning of the source assembly for effective radiation therapy and is a substantial improvement over the prior art.